The invention relates to a method for hard fine machining of a workpiece with a worm-shaped cutting tool, wherein the workpiece comprises an axis and is supplied with a profiling along its circumference, wherein the cutting tool comprises an axis and is supplied with a machining surface, wherein a hard machining process of the profiling is carried out at simultaneous synchronized rotation of the workpiece around its axis and of the cutting tool around its axis with given meshing of the machining surface into the profiling by moving the cutting tool in the direction of the axis of the cutting tool and wherein a shift movement is superposed to the cutting tool in the direction of the axis of the cutting tool during the hard machining process.
At hard fine finishing, particularly of gears, the grinding with a grinding worm is well known in the state of the art. It is referred to EP 1 987 919 A2 in an exemplarily way, where a grinding worm is described to the mentioned purpose. Herewith a continuous grinding process takes place (in contrast to the discontinuous grinding of the individual tooth gap of the gear which has to be grinded), wherein the grinding worm meshes with the gear which has to be grinded and the gear and the grinding worm rotate relatively to another in a correlating manner with the appropriate infeed.
Thereby, at generative grinding of a toothing and a profile respectively it can be provided that the grinding worm is displaced (so called “shifting”) in its axial direction during the machining (i. e. while the worm is guided in axial direction of the gear with a respective infeed) to compensate the wear of the grinding worm. The electronic gearbox of the grinding machine, which ensures the precise synchronized rotation between the grinding worm and the workpiece, guarantees thereby the coupling of the volution, taking into account the planned and programmed shift movement.
For each workpiece a defined worm region of the grinding worm is provided at the machining. From this results the number of parts to be grinded between two dressing processes. Normally, the mentioned shift amount is calculated in such a manner that all parts between two dressing processes (i. e. the parts per dressing) correspond to the required quality and that a maximal productivity is obtained.
At the grinding without the mentioned shifting respectively at shifting with low shift amounts a regular structure is formed at the flank surface of the teeth of the gear, wherein the grinding marks run parallel to another along the whole width of the workpiece. Such a structure influences negatively the noise behavior during meshing of the gear pairs in the gearbox. To improve the noise behavior methods have been developed which modify the surface structure so that the parallel running grinding marks are interrupted or do not exist anymore at all. The surface structure is then characterized by the offset arrangement of the grinding marks in the direction of the profile.
In EP 1 600 236 B1 another approach is used at which the movement of the workpiece along the tooth width is chosen unequally.
WO 2007/139708 A2 describes a solution at which by shifting different axial regions of a grinding worm are brought into contact to compensate modifications in the diameter of the grinding worm caused by wear. Also, JP H06 15527 A employs a shift movement of a grinding tool to use the tool life in an optimal manner.
All pre-known methods are either laborious or do not deliver the desired effect.